The present application relates to europium-activated yttrium vanadate (YVO4:Eu) doped with Tb and/or Sm, a fluorescent lamp using the YVO4:Eu, and a display, device and an illuminating device using a fluorescent lamp.
Fluorescent lamps are used as backlights of liquid crystal displays for televisions and PC and coated with various phosphors. Phosphors are also used for various displays other than liquid crystal displays.
In order to win competition with plasma display panels (PDP) and other flat panel displays (FPD), further discrimination is required for liquid crystal displays (LCD). A large factor of discrimination is image quality, and there is keen competition among various types of FPD with respect to luminance, color gamut contrast, motion picture properties, and the like. Among these, the color gamut and luminance are generally contrary to each other. Namely, when the color gamut is extended, the emission wavelengths of a phosphor contributing to emission of a blue light component and a phosphor contributing to emission of a red light component may be shifted to a lower wavelength and a longer wavelength respectively, thereby decreasing luminance in a direction away from the human visibility. In order to extend the color gamut and maintain or improve the luminance, it is desired to use a high-efficiency phosphor or increase the luminous efficiency of the phosphor used.
Display colors of LCD are formed by separating white light, which is emitted from a backlight mainly composed of a fluorescent lamp (a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL), or a flat fluorescent lamp (FFL)), using blue, green, and red color filters.
A fluorescent lamp is generally coated with phosphors which emit three color lights (in some types, three or more color lights) such as blue light, green light, and red light. The color gamut is, strictly speaking, related to the transmission properties of a liquid crystal portion constituting LCD, but it is basically determined by the transmission properties of a color filter constituting LCD and the emission properties of light emitted from a backlight.
There are active attempts to extend the color gamut of LCD by improving or optimizing a phosphor used in a fluorescent lamp.
Japanese Unexamined Patent Application Publication No. 2005-332625 (paragraphs [0006] to [0010]) entitled “Fluorescent Lamp and Display Device” discloses a fluorescent lamp having a configuration capable of securely suppressing the occurrence of a difference between the compositions of phosphor particle mixtures at both ends of a glass tube and a display device including the fluorescent lamp.
Japanese Unexamined Patent Application Publication No. 2006-322991 (paragraphs [0012] to [0013]) entitled “Liquid Crystal Display Device” discloses a liquid crystal display device capable of extending a color reproduction range when a cold cathode fluorescent lamp is used as a light source.
Japanese Unexamined Patent Application Publication No. 2006-196374 (paragraphs [0010] to [0020]) entitled “Backlight Device and Liquid Crystal Display Device” discloses a backlight device capable of realizing a wider color gamut of a liquid crystal display device with little decreasing a luminescent value and a liquid crystal display device including the backlight device.
A typical example of wide-color-gamut fluorescent lamps uses BaMgAl10O17:Eu or (Sr, Ca, Ba, Mg)5(PO4)3Cl:EU as a blue phosphor, BaMgAl10O17:Eu, Mn as a green phosphor, and YVO4:Eu, Y(V, P)O4:Eu, or 3.5MgO.0.5MgF2.GeO2:Mn as a red phosphor.
Among these colors, red has high attractiveness and easily attracts attention, and thus a large improvement effect is expected. A red phosphor YVO4:Eu for wide-color gamut fluorescent lamps has an emission peak at 620 nm which is longer than the emission wavelength of 611 nm of ordinary Y2O3:Eu, and thus red chromaticity may be improved.
With respect to a red light-emitting phosphor. Japanese Unexamined Patent Application Publication No. 2001-226672 (claims 1 to 3 and 8 paragraphs [0048] and [0056]) entitled “Phosphor with Improved Lumen Maintenance Factor” describes the following;
(1) A composition containing YMO4:Eu, L (wherein M is at least one of vanadium and phosphorus, and L is at least one of trivalent rare earth ion species excluding Eu and divalent metal ion species).
(2) The composition described in (1) wherein Eu is an ion with a valence of +3.
(3) The composition described in (1), containing (Y1-x-zDxTz)MO4:Eu (wherein 0≦x≦0.05, 0≦z≦0.02, D is at least one of divalent metal ion species, and T is at least one of trivalent rare earth ion species excluding Eu).
(4) The composition described in (3), containing (Y1-qTbq)VO4:Eu (wherein 0<q≦0.02).
In order to prove the effect of improving lumen maintenance by adding trivalent rare earth ions, the characteristics of (Y, Tb)VO4:Eu3+ phosphor (Y0.9497Eu0.05Tb0.0003VO4) were examined by TTL. A Y0.949Tb0.001Eu0.05VO4 phosphor was prepared by a liquid phase flux method.
The emission properties and the like of phosphor YVO4:Eu are described in “Phosphor Handbook” edited by Phosphor Research Society first edition, OHMSHA, Ltd, 1987 (pp. 233-235).
With respect to phosphor YVO4:Eu, “Strong Quenching of Tb3+ Emission by Y—Tb Interaction in YPO4-YVO4”, J. Chem. Phys., 53(2), 681-685 (1970) (INTRODUCTION) describes that YVO4:Eu emits light, while YVO4:Tb does not emit light.